1. Field of the Invention
The invention relates to coating materials for pharmaceutical dosage forms which are soluble or swellable in gastric juices, and more particulaly to such coating materials which contain as binders polymers of aminoalkyl esters of acrylate or methacrylate acids and optional additional co-monomers prepared by emulsion polymerization.
2. Description of the Prior Art
Binders of this general type are known from German Pat. No. 2,135,073. The aminoalkyl esters therein disclosed for preparing such polymers by emulsion polymerization uniformly contain 2 carbon atoms between the amino-nitrogen atom and the ester-oxygen atom. The only disclosed co-monomer departing from this structure is the 4-(dimethylamino)butyl ester. In the preparation of the polymers from these monomers by emulsion polymerization, difficulties can arise because these monomers are readily soluble in water, especially the most commonly used one, dimethylaminoethyl methacrylate. A portion of the monomers can homopolymerize in the aqueous phase to form water-soluble homopolymers, and if these become bound to the latex particles or enclosed in them in the course of polymerization, they can greatly effect the solubility of the pharmaceutical coatings prepared from the latex. Furthermore, these monomers having short or unbranched alkylene groups in the aminoalkyl radical have a tendency to hydrolyze, which can occur any time before the monomer is incorporated into the polymer. As a result of this hydrolysis, acrylic or methacrylic acid is formed which is also incorporated into the polymer and alters the solubility properties. Because of these drawbacks, polymers containing more than 55% by weight of aminoalkyl esters of this type could not be prepared by emulsion polymerization, and those which contain more than 30% by weight of aminoalkyl esters can be prepared only with difficulty.
Therefore, a need has continued to exist for polymers suitable for use as binders in pharmaceutical coating materials, which can be prepared by emulsion polymerization, and which are not subject to the drawbacks of the known emulsion polymers which are used for this purpose.